Squid + Multiple IPv6 Setup

I have a VPS running KVM + Ubuntu with 1 x IPv4 and 25 x IPv6. I have Squid3 setup using username/password allowing users to connect and use the IPv6. This is shown below (IPs shown are for demonstration purposes only): acl myaccount1 proxy_auth user1 acl myaccount2 proxy_auth user2 acl manager proto cache_object http_access allow ncsa_users http_access allow myaccount1 myaccount2 http_access allow all tcp_outgoing_address 2607:f878:1:34b:0:11:49:1 myaccount1 tcp_outgoing_address 2607:f878:1:21b:9:42:87:1 myaccount2 However, I am unable to assign different users a different IPv6. Even if [login to view URL] uses tcp_outgoing_address to specify a different IPv6 for each user account, the same IPv6 is shown regardless of which account I login with. I need someone to show me what I am doing wrong so that my user accounts have a different IPv6 when surfing a website that tests/shows what your new IPv6 is. Ideally, 25 user accounts should all be assigned five different IPv6 that are available on my VPS. You don't have to setup all these 25 x accounts, but need to show me what I am doing wrong so I can make different users assigned a different IPv6.